\documentclass{standalone}
\usepackage{enumitem}
\usepackage{tikz} % Required for drawings
\usetikzlibrary{shapes}
\usetikzlibrary{arrows}
\usetikzlibrary{calc}

\definecolor{mygreen}{rgb}{0,0.6,0}

\begin{document}
	\tikzstyle{state}=[draw,shape=circle]
	\tikzstyle{gstate}=[draw,shape=circle,mygreen]
	\tikzstyle{edge}=[draw,latex'-]
	\tikzstyle{gedge}=[draw,latex'-,mygreen]
	\centering
	\begin{tikzpicture}
		\draw[opacity=0.0,very thick] (0.5,4) rectangle (3.5,-1);
		
		\node at (1,4.5){$\mathcal{S}_0$};	
		\node at (2,4.5){$\mathcal{S}_1$};
		
		\node[gstate] (s00) at (1,0) {};
		\node[gstate] (s01) at (1,1) {};
		\node[gstate,ultra thick] (s02) at (1,2) {};
		\node[gstate] (s03) at (1,3) {};
		
		\node[state] (s10) at (2,-0.5) {};
		\node[state] (s11) at (2,0.5) {};
		\node[state] (s12) at (2,1.5) {};
		\node[state] (s13) at (2,2.5) {};
		\node[state] (s14) at (2,3.5) {};
		
		\draw[edge] (s00) -- (s10);
		\draw[edge] (s00) -- (s11);
		\draw[edge] (s00) -- (s12);
		\draw[edge] (s02) -- (s13);
		\draw[edge] (s02) -- (s14);
		
		\draw[mygreen,very thick] (0.5,4) rectangle (1.5,-1);
	\end{tikzpicture}
\end{document}
